How Can I Find Matching Records Across Multiple Tables in MySQL Without Using INTERSECT?

Finding Record Intersections in MySQL Using INNER JOIN and IN Clause

When working with multiple tables, it often becomes necessary to search for records that match certain criteria across multiple fields. In this scenario, you want to find records where the firstname and lastname fields match specific values in another table.

One approach is to use the INTERSECT command, as seen in your SQL query example. However, MySQL does not support INTERSECT. Instead, there are alternative methods to achieve the desired result.

Using INNER JOIN

An INNER JOIN can be used to filter records that have matching rows in another table. In your case, you can use the following query:

SELECT DISTINCT records.id
FROM records
INNER JOIN data d1 ON d1.id = records.firstname AND d1.value = "john"
INNER JOIN data d2 ON d2.id = records.lastname AND d2.value = "smith"

This query will return the unique IDs of records that satisfy both conditions.

Using IN Clause

Another alternative is to use the IN clause to filter for values that exist in a subquery:

SELECT DISTINCT records.id
FROM records
WHERE records.firstname IN (
    SELECT id FROM data WHERE value = 'john'
)
AND records.lastname IN (
    SELECT id FROM data WHERE value = 'smith'
)

This query will return the same result as the INNER JOIN query by selecting records where the firstname and lastname values match the specified values in the subqueries.

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